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  • Author Author: baldengineer
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Are you still using 7400-Series Logic, if so, where?

baldengineer

Over the past several months, I have been learning about and repairing 8-bit computer and video game systems. So far, I have worked on the VIC-20, C64, ZX-81, Apple II, and have been learning about the TI 99/A.

 

It always amazes how much of these early computer systems were built almost entirely with standard 7400-series (LS and HC) chips.

 

Occasionally, I need to replace a 7400-series chip. (I always hope it is one of those and not one of the ASICs!) While looking for modern replacements, I have noticed the trend that they are becoming more scarce. The LS-series is almost entirely gone--and with good reason. While HC and HCT continue to be somewhat available, they are usually only available in surface-mount packages.

 

That leads me to the question: Who is still using the venerable 7400-series logic chips today?

 

To me, there are three groups that might be using them:

  1. Learning. Students and hobbyist learning about digital logic
  2. New Design. Hardware that needs glue-logic. Are these using multi-gate chips or the single-gate variants?
  3. Repair. Older electronics in need of replacements. Here is where I mostly sit.

 

Do you fit into one of those categories? If not, where do you land?

 

And THEN, which chips are the must-have on-hand?

Obviously, the answer depends on how you might be using them. But, I'm curious to know how you use 7400-series chips and which ones would you keep in stock?

  • Yes, for 8-bit microcontrollers the 74HC595 parallel output shift-register is a cheap way to get more outputs, along with the 74HC165 parallel input shift-register for extra inputs. I also like the 74HC4050 hex buffer to get 5V logic inputs for 3V3 µCs.

     

    For modern microcontrollers the 74LVC series have many 3.3V or 5.5V input tolerant ICs that operate down to 1.65V, such as the 74LVC245 octal transceiver. This series also include single logic-gate chips such as the 74LVC1G08 AND-gate which can get you out of a pickle in a mixed voltage system.

     

    As for what I keep in stock is just whatever I have left over from older orders, along with the 74-series and 4000-series logic ICs in DIP that I've been buying whenever someone has been clearing out their old stuff.

    image

  • ps, for those interested in playing with logic... https://simulator.io/   is a pretty handy simulator.

     

    But if I recall correctly, not all 7400-series chips are logic - I remember some counters and shifters too.

     

    Oh that reminds me - I used shift registers for my version of an OpenSprinkler.org sprinkler board! And I think OpenSprinkler does too for their own boards.

    74HC959 - also still recommended for expanding IO on boards like Arduino. See Oomlout tutorial too: products:ardx:circ-05[.:oomlout:.]

     

    Kinda like the 555 chips - too handy to not use once in a while.

     

    Best,

    -Nico

  • in reply to dougw

      wrote:

     

    I still have some 7400 parts but I have more 4000 (CMOS) series parts.

     

    Right! the CD4000 kind of somethings... are those the ones that work with higher voltages?

  • Yes, I do!

    I have tens of 74xx ICs kept pricked to a thermocol slab and occasionally use them to cross-check few designs or simply to play around. I think because they are of low cost, easy to understand and use, it's still used in educational institutions and probably they have the majority of worlds 74xx stocks.

  • Since I do a lot of salvage of older boards I have quite a few 74 series logic chips. I checked my inventory and I have about 50 different bins with a mixture of series in some of the bins. I will keep the 74xx, 74HCxx, 74LSxx, etc chips together in one bin and then go looking for the series I want for a specific project.  I use them occasionally in builds and even more occasionally in repairs as they really are quite hardy. Once in a while I come across a number that I didn't have before and I get excited like I did as a kid when I would find a penny that fit in an open hole in the penny collect folder.